Global genetic capacity for mixotrophy in marine picocyanobacteria

12 pages, 6 figures, 2 tablesThe assimilation of organic nutrients by autotrophs, a form of mixotrophy, has been demonstrated in the globally abundant marine picocyanobacterial genera Prochlorococcus and Synechococcus. However, the range of compounds used and the distribution of organic compound uptake genes within picocyanobacteria are unknown. Here we analyze genomic and metagenomic data from around the world to determine the extent and distribution of mixotrophy in these phototrophs. Analysis of 49 Prochlorococcus and 18 Synechococcus isolate genomes reveals that all have the transporters necessary to take up amino acids, peptides and sugars. However, the number and type of transporters and associated catabolic genes differ between different phylogenetic groups, with low-light IV Prochlorococcus, and 5.1B, 5.2 and 5.3 Synechococcus strains having the largest number. Metagenomic data from 68 stations from the Tara Oceans expedition indicate that the genetic potential for mixotrophy in picocyanobacteria is globally distributed and differs between clades. Phylogenetic analyses indicate gradual organic nutrient transporter gene loss from the low-light IV to the high-light II Prochlorococcus. The phylogenetic differences in genetic capacity for mixotrophy, combined with the ubiquity of picocyanobacterial organic compound uptake genes suggests that mixotrophy has a more central role in picocyanobacterial ecology than was previously thought.We thank the US National Science Foundation OCE postdoctoral research fellowship program and the Fulbright Commission, Spain for supporting APY. The work was also supported in part by the European Molecular Biology Laboratory, grants to SWC from the Gordon and Betty Moore Foundation (grant GBMF495) the National Science Foundation (grants OCE-1356460 and DBI-0424599), grants from the Simons Foundation (grant 337262), the Spanish Ministry of Science and Innovation grant to SGA, CGL2011-26848/BOS MicroOcean PANGENOMICS and U FP7-OCEAN.2011-2. Micro3B Marine Microbial Biodiversity, the Bioinformatics and Biotechnology Large Collaborative grant 287589 and is a contribution of the Simons Collaboration on Ocean Processes and Ecology (SCOPE)Peer Reviewe